Concrete Formwork Basics

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Questions and Answers

What is the primary benefit of using metal clamps or special wedge pin connections in formwork?

They are costly to produce and maintain.

They complicate the formwork process.

They provide secure connections that are easy to assemble and dismantle. (correct)

They require special tools for assembly.

What is the primary purpose of formwork in concrete construction?

To mold the concrete into a desired size and shape (correct)

To allow for immediate curing of the concrete

To permanently shape the concrete once poured

To support the structure during the entire construction period

Which material was previously the most common for formwork?

Concrete

Lumber (correct)

Plastic

Metal

Why should the size of form sections be limited to the capacity of the largest crane planned?

To ensure efficient handling and lifting operations. Signup and view all the answers

What is a disadvantage of high lifts in wall construction?

They cause placement and vibration difficulties. Signup and view all the answers

What is a limitation of timber formwork?

It has a short lifespan and is time-consuming to produce Signup and view all the answers

How has modern formwork technology enhanced construction practices?

By promoting the use of prefabrication and reuse of forms Signup and view all the answers

Which of the following describes the function of ties in formwork?

To hold the form sides together against fluid pressure. Signup and view all the answers

Under what condition can bending stresses for lumber be increased by 25%?

For short duration loads lasting approximately 7 days or less. Signup and view all the answers

What are some objectives of building forms in concrete construction?

To ensure safety, quality, and economy Signup and view all the answers

What challenge does formwork disassembly often face?

Concrete bond, shrinkage, and rigidity restrict it Signup and view all the answers

What is the role of the wales in a concrete formwork system?

To support the studs and distribute loads. Signup and view all the answers

What design consideration is important for reinforcement during formwork installation?

Rebar cages can be pre-assembled before installation. Signup and view all the answers

What type of formwork involves prefabricated modules?

Modular or prefabricated formwork Signup and view all the answers

Which of the following is NOT considered an objective of formwork?

Aesthetic customization Signup and view all the answers

Which of the following statements about anchors in formwork is correct?

Anchors are embedded in previously placed concrete to support formwork. Signup and view all the answers

What is a key characteristic of Stay-In-Place Structural Systems?

They remain in place after the concrete has cured. Signup and view all the answers

Which quality must formwork possess to ensure the desired shape of the concrete is maintained?

It must be rigid under construction loads. Signup and view all the answers

What happens to wood when the moisture content exceeds 19%?

It softens and is less able to carry stresses. Signup and view all the answers

What is the effect of designing formwork for maximum reuse?

It may increase initial cost but could reduce total costs over time. Signup and view all the answers

What is a significant factor that contractors must plan for when bidding on a project involving concrete formwork?

The total cost of formwork materials. Signup and view all the answers

How does increasing the cross-sectional size of lumber affect allowable stresses?

It increases allowable stresses. Signup and view all the answers

What is the purpose of the Horizontal Shear Constant (CH) in lumber?

To account for lumber defects at the beam ends. Signup and view all the answers

Which of the following is NOT a consideration when preparing formwork?

The overall aesthetics of concrete. Signup and view all the answers

How can shop-built forms provide an advantage in formwork construction?

They allow for greater efficiency in material usage. Signup and view all the answers

Which factor is NOT considered important regarding lateral pressure of concrete?

Size of form cross section. Signup and view all the answers

What role does form stability play in concrete construction?

It ensures alignment and support of large concrete members. Signup and view all the answers

What is a key characteristic of plywood mentioned in formwork design?

It provides smooth, finished surfaces on concrete. Signup and view all the answers

What is a potential drawback of using prefabricated forms?

They may have limitations in custom shapes and sizes. Signup and view all the answers

What is the significance of the Rolling Shear Constant in plywood?

Calculates rolling shear stress when loads are applied perpendicular to the panel. Signup and view all the answers

Under which condition does temperature adjustment occur for allowable stresses?

For temperatures exceeding 100ºF. Signup and view all the answers

What should be used for calculating deflection in plywood without calculating moment of inertia?

Tabulated section properties. Signup and view all the answers

Study Notes

Formwork for Concrete

Formwork is a temporary structure that molds and supports freshly poured concrete until it sets and becomes self-supporting.
Development of formwork has evolved alongside concrete construction in the 20th century due to increased utilization of concrete as a primary construction material.
Components of formwork, including connections, braces, and anchorages, are also temporary.
Formwork materials must be durable and maintainable, as they are reused multiple times.

Types of Formwork

Timber Formwork: Traditionally made on-site from lumber and plywood; labor-intensive with a shorter lifespan. It's flexible and more economical in regions with low labor costs.
Prefabricated Modular Formwork: Constructed off-site and easily assembled; made from steel, aluminum, or high-density plastics. Offers durability and improved surface finish.
Stay-In-Place Structural Systems: Utilize prefabricated materials and remain permanently in position post-concrete curing. Suitable for columns, piers, and bridge decks.

Formwork Design and Goals

Proper design maximizes reuse while ensuring safety and quality.
Critical objectives include maintaining strength, alignment, and dimensions during and after material placement.
Forms must be rigid under loads, stable for alignment, and capable of enduring repeated handling.

Economic Considerations and Techniques

Significant percentages of construction costs are attributed to formwork; planning during bidding is essential.
Strategies to economize:
- Design forms for maximum reuse.
- Use shop-built forms for efficiency.
- Consider rental options for prefabricated forms.
- Utilize cranes effectively to handle large load sections.
- Optimize concrete placement by avoiding high lifts to reduce complications.

Form Materials and Properties

Plywood is commonly used, known for its economical large panels and smooth surface finish.
Key properties of lumber, such as allowable stresses, moisture effect, and size adjustments, must be considered in the design of formwork.
Plywood's performance is enhanced with cross banding, offering strength in two dimensions.

Loads and Forces on Formwork

Fresh concrete exerts hydrostatic pressure as it behaves like a fluid during placement.
Factors influencing lateral pressure include concrete mixture density, temperature, placement rate, and use of admixtures.
Understanding allowable stresses in wood is crucial for ensuring formwork integrity, including adjustments for load duration, moisture, and temperature.

Essential Components of Formwork

Ties: Hold concrete forms together under fluid pressure; designed for partial or complete removal.
Anchors and Clamps: Used to support and position formwork against lateral pressures.
Ensure plywood and lumber are free from defects to maintain allowable stresses and prevent failure during the construction phase.

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Description

Explore the fundamentals of formwork used in concrete construction. This quiz covers the types of formwork, their functions, and the importance of temporary molds in shaping concrete. Test your knowledge on how formwork has evolved alongside concrete technology.